Polyvinyl alcohol is the largest volume, synthetic, water-soluble and biodegradable resin produced in the world. Its success is due in part to its excellent chemical resistance and physical properties as well as to its very low toxicity. The main applications for polyvinyl alcohol are in textile sizing, adhesives, polymerization stabilizers and paper coatings. As demand increases for better performance in these and other areas, more attention is given to production of polyvinyl alcohol derivatives which can meet the demand. Modification of polyvinyl alcohol by introducing functional groups (for example, sulfonates, phosphates and carboxylates) through copolymerization or post-modification is one means of enhancing the physical properties of polyvinyl alcohol.
Copolymerization of vinyl acetate with functional vinyl monomers followed by saponification is a well-known route to modification of polyvinyl alcohol. Some applications of this technology are exemplified in the following patents:
JP 56-73199 teaches copolymerization of vinyl acetate with 2-acrylamido-2-methylpropanesulfonic acid or its metal salts, to produce a polymer with improved flow properties for application in paper coatings.
U.S. Pat. No. 4,529,522 teaches production of copolymers of polyvinyl alcohol and ethylene oxide or propylene oxide sulfonate ethers for use as viscosifiers i n saline solutions.
JP 60-56196 teaches copolymerization of vinyl acetate with 0.1 to 0.3 mole percent sodium vinyl sulfonate or sodium allyl sulfonate and hydrolysis of 30 to 60 percent of the resulting copolymer. The product can be used in hot melt adhesives.
JP 63-270704 teaches the manufacture of high polymerization degree sulfonic acid-containing modified polyvinyl alcohol by copolymerizing N-sulfoalkyl(meth)acrylamide and vinyl ester and then saponifying the resulting copolymer. The products are useful as emulsifiers.
The secondary hydroxyl groups in polyvinyl alcohol can be used as an active site for modification. Examples of these reactions can be found in Polyvinyl Alcohol, edited by Finch (Wiley, 1973), pages 183-202. Most of the reactions are carried out in aqueous or organic solution and do not result in a solid product. The energy costs associated with preparing the initial solution and in reducing the product to a solid makes most of these modification processes prohibitively expensive. Following are examples of patents on solution modification procedures.
EP-128,345 teaches the reaction of polyvinyl alcohol with alkenal3-sulfonic acid in aqueous solution to form a product used in textile sizing or emulsifiers.
U.S. Pat. No. 4,545,911 teaches grafting pyrrolidium methane sulfonate salt onto the alcohol oxygens of polyvinyl alcohols to form viscosifiers which are useful in waterflooding and in drilling fluids.
Michael-type addition for the reaction of compounds containing activated carbon-carbon double bonds with polyvinyl alcohol is known. U.S. Pat. No. 3,505,303 teaches the reaction of polyvinyl alcohol with acrylamide in a combination slurry/solution process resulting in modification at the hydroxy group of the polyvinyl alcohol and the beta-position of acrylamide.
GB 2,199,834 teaches modification of polyvinyl alcohol with acrylamide and other alpha, beta-unsaturated carbonyl compounds in a water slurry.
Articles by Imia, et al. (J. Mocromol. Sci.-Chem., Vol .A22, No.10, pages 1359-1369, 1985 and J. Appl. Polym. Sci., Vol.35, pages 1817-1828, 1985) describe Michael -type addition of sulfones and sulfoxides to polyvinyl alcohol. The reaction takes place in an aqueous solution.
A few post-modification processes for slurry or solid state reactions are also known. U.S. Pat. No. 3,125,556 teaches the alkoxylation of polyvinyl alcohol in which an organic polar swelling agent may be added to the polyvinyl alcohol prior to alkoxylation.
U.S. Pat. No. 4,775,715 teaches preparation of cationic polyvinyl alcohol by blending polyvinyl alcohol under high shear conditions, at 0.degree. to 100.degree. C. with a small amount of water, a small excess of base, and a quaternizing agent. JP 1-34245 teaches a method for preparing a polyvinyl alcohol type resin containing an acetoacetic ester by mixing a finely divided polyvinyl alcohol powder with diketene in a high intensity mixer.
U.S. Pat. No. 4,822,851 and U.S. Pat. No. 5,001,191 teach a dry blending process for the preparation of cationized polyvinyl alcohol in which polyvinyl alcohol, preferably in powder form, reacts with alkylidene epoxides in an alkaline medium in the presence of water.
SU 1,654,301 teaches the reaction of dried polyvinyl alcohol with caprolactam in the presence of powder zinc or lead in order to form a grafted copolymer.